The fabrication of semiconductor circuits has been greatly facilitated by the use of plasma reactors, and similar equipment. In fabricating semiconductor integrated circuits, such equipment is employed for depositing layers or films of conductive material, semiconductor material or insulating materials in various patterns and configurations to form microcircuits. Dry etching of semiconductor materials can also be conducted with chemical vapor transport systems to selectively remove desired areas of such materials. Generally, a number of identical and individual integrated circuits are fabricated on a circular semiconductor wafer or slice. Well-known batch reactors are constructed to accommodate a number of such slices in a single reaction chamber and thereby simultaneously perform the material deposition or etching of all the slices.
More recently, single slice processing reactors have been developed to increase the product uniformity in accordance with current advanced semiconductor processes. The small chamber of a single slice reactor enables easier control of the operating variables, such as gas flow and energy distribution, than the larger chambers of the multi-slice batch reactors. However, undesirable pressure and flow gradients within the single slice reactor can be larger, especially in the vicinity of the slice, due to the close proximity of the reactor chamber vacuum ports and injection nozzles to the slice. This condition necessitates the utilization of equipment for controlling such gradients.
Heretofore, shower head apparatus has been utilized for dispersing the reactant gases over the slice so as to provide a uniform flow thereover. Notwithstanding, such shower head equipment does not address the problems of the nonuniform distribution of gases in the plasma due to the location of vacuum ports through which the spent gas is withdrawn from the reaction chamber. With such shower head apparatus, nonuniformity in the material deposition or etch rate may occur during the chemical vapor transport process. Conventional single slice, parallel electrode reactors inject reactant gases into the reaction chamber through one of the noted electrodes. Sintered stainless steel disks having a uniformly porous structure comprise such electrodes, and pressure gradients are employed to force the diffusion of gases through such electrode. More commonly, nonporous disks having uniformly spaced holes therein are utilized as the electrode structure. This type of apertured disk is common in many plasma reactors in current use today. U.S. Pat. No. 4,534,816 discloses such a plasma reactor with an apertured electrode disk having uniformly spaced and sized holes formed therein.
The plasma reactor of the noted patent relies on the injection of a gas and two pressure drops therein for ensuring uniformity of flow. The first pressure drop occurs across a baffle upstream from the electrode which produces the second pressure drop. With this structure, it is attempted to inject the gas uniformly over the entire surface of the slice, without addressing the radial nonuniformities which form as the gas is evacuated around the circumference of the slice. The flow is therefore radially nonuniform from the center of the slice to the circumferential edge thereof. The disadvantage of this radial outward flow is the nonuniformity of various process parameters which occur due to the pressure gradient existing over the surface of the slice. As a result, the deposition of a layer of material in the center of the slice may be thicker than that which is deposited near the edge of the slice. The various integrated circuits fabricated on the slice may then exhibit different electrical characteristics.
From the foregoing, it can be seen that a need exists for an improved plasma reactor which provides a uniform dispersion of plasma gases over the surface of the slice to thereby provide an overall uniform depth of material deposited or etched therefrom. A further need exists for apparatus for use with plasma reactors for providing a uniform distribution of plasma gases in a desired pattern for depositing material only on selected surfaces of the slice.